Heat Exchanger

Possible problem, added coolant to the engine which was a little low. Brought it to the top,yellow coolant and ran the engine for 30-40 minutes. Checked the coolant level again and noticed it was full but with what looked like sea water. Could it be the heat exchanger is shot ? Engine has about 2500 hours on it and looks like it might be the original. Only had the boat for a couple of months and just pulled the zinc out of the exchanger and to my surprise no zinc at all. Any advice would help.
Thanks

Coolant colors are deceptive. Hard to tell much from color. Take zincs out of heat exchanger and pressure test whole cooling system. If it is leaking, whatever coolant you have will come out the zinc holes.

You could also have the return coolant tested by an analytical laboratory. Ethylene glycol versus salt water.

Remove the hx and pressure test it. It probably needs to be cleaned anyways if it is not leaking... cleaning the hx should be on the shortlist with any new to you boat.

Ski in NC said:

Coolant colors are deceptive. Hard to tell much from color. Take zincs out of heat exchanger and pressure test whole cooling system. If it is leaking, whatever coolant you have will come out the zinc holes.

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I like this method....sooooo simple!!!

gonesailing13 said:

Possible problem, added coolant to the engine which was a little low. Brought it to the top,yellow coolant and ran the engine for 30-40 minutes. Checked the coolant level again and noticed it was full but with what looked like sea water. Could it be the heat exchanger is shot ? Engine has about 2500 hours on it and looks like it might be the original. Only had the boat for a couple of months and just pulled the zinc out of the exchanger and to my surprise no zinc at all. Any advice would help.
Thanks

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I had this problem last year. I noticed it because my coolant overflow can was filling.
The sea water pressure was higher than the engine coolant pressure. When the heat exch developed a leak the higher sea water pressure filled the engine cooling loop with sea water. Picked up a pair of re-man heat exch and then flushed the engines half a dozen times with radiator flush until clean and filled with coolant.

Just curious re FL heat exchangers and other FL parts. So often (on Ebay for example) parts for the FL 120 seem readily available whereas parts for the FL 135 seem scarce. Are most FL 120 parts interchangeable with the FL 135 and if so where can an interchangeable parts list be found?
Thanks

I can't answer about the interchanging parts but we've had no problem getting them for our FL SP135 in the last 10 plus years. We just had the engine rebuilt from top to bottom and everything was available, even new pistons.

petdoc4u said:

Just curious re FL heat exchangers and other FL parts. So often (on Ebay for example) parts for the FL 120 seem readily available whereas parts for the FL 135 seem scarce. Are most FL 120 parts interchangeable with the FL 135 and if so where can an interchangeable parts list be found?
Thanks

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There do seem to be more "random" people selling FL120 parts than 135 parts. I think it may be that since the FL120 has been around a lot longer there are more 120's being retired. That said, I have found a number of good sources for 135 parts.

As far as interchangability goes, most FL120 parts are not interchangable with 135's. The exceptions (that I can think of right now) are the raw water pump(but not the drive gear), the lift pump, alternator, starter, oil and xmission coolers (but not the engine HE).

Ken

You can use pretty much any heat exchanger - as long as its big enough. They were just chosen for cost for the original engines and they should be serviced regularly anyway. I bought new ones and kept the old for spares which I intended to rotate through every few years.

You can't overcool the engine with a working thermostat.